The Hawke's Bay District Health Board (HBDHB) is warning people not to swim in Lake Tutira and Waipatiki Lagoon.
Staff have been sent to investigate Lake Tutira, north of Napier after cyanobacteria algal blooms were discovered.
HBDHB said some cynobacteria species produce toxins which pose a risk to
humans and animals.
Medical officer of health Caroline McElnay warned people not to swim in the lake or to drink water from it. She said pets should also be steered clear.
Symptoms of contact with the bloom include severe skin rash, upset stomach, hay fever and asthma attacks.
A health board spokeswoman said the bloom can make the water appear murky and may give off a musky odour.
A warning has also been issued for Waipatiki Lagoon, also north of Napier, which has raised levels of E.coli after heavy rains upstream washed effluent from farmland and discharges down various tributaries.
A media release from the health board said tests done on Christmas Eve showed E.coli levels which "significantly exceed the maximum levels recommended [with] excessive amounts of faecal matter".
Dr McElnay said people should always check waterways for clarity (generally a sign it is not contaminated) before swimming.
"A quick test is can you see your feet when knee deep in the water?"
According to the health board's website, the lagoon often exceeds bacteria levels recommended for safe swimming and is not generally safe for swimming.
- NZPA
